Neutron ray generators have recently been developed for a variety of uses. Most conventional neutron generation systems are employed in the technique of neutron activation analysis in which high energy (fast) neutrons generated by directing an ion beam in an accelerator tube are directed at a suitable target which then emits high energy neutrons. The composition of the test material radiated with high energy neutrons is determined by analyzing the emissions therefrom.
In other applications, such as neutron radiography or in some instances neutron ray therapy, high energy (fast) neutrons are not suitable, and such fast neutrons must be reduced to lower energy (thermal) neutrons by discharging a high energy neutron beam into a suitable moderator medium. Since the thermalized neutrons produced in the moderator medium are randomly scattered and isotropic, a directional component of the thermal neutrons must be collected to provide a directed neutron beam. Furthermore, since substantial background neutron, X-ray and gamma ray radiation cannot be tolerated in neutron radiography or neutron ray therapy applications, a thermal neutron collimator is needed for providing a highly directed thermal neutron beam without substantial background neutron, X-ray, gamma ray, or fast neutron radiation. Such a collimator must be effective when used with neutron generator sources having primary neutron energies as high as approximately 14 million electron volts (MeV).